This invention relates to an illuminator for a document scanning system of a copying machine. More particularly, the invention relates to apparatus to concentrate a line of intense light on a document for optical readout of the light reflected from the document.
Typical prior art illuminators are exemplified by the following patents and publications. Peterson U.S. Pat. No. 4,239,383 discloses primary and secondary elliptical reflectors to concentrate a line of light from a lamp in a narrow band. A third flat reflector reflects a portion of the light from the light source which would not otherwise be directed into the narrow band back into the primary and secondary reflectors to be reflected into the narrow band of light. Maddox U.S. Pat. No. 4,095,881 discloses an illuminator having a lamp at one focal point of an elliptical cylinder and an interference filter for separating the IR radiation and redirecting the IR rays back to the incandescent lamp for further heating the lamp. Hamaguchi U.S. Pat. No. 3,947,115 discloses two right elliptical cylinders of different ellipticity with a common line foci. A line light source is positioned at the other foci of the first, and the other foci of the second is positioned on the material being copied. Young U.S. Pat. No. 3,302,519 discloses an illuminator comprising sections of two different size cylindrical ellipses having common focal points with the line light source at one and the copy line at the other. The reflection for the copy passes in the offset between the ellipses. IBM Technical Disclosure Bulletin Vol. 14, No. 11, April 1972, at page 3236, Baxter et al in "Document Illuminator Using Elliptic and Dichroic Reflectors" discloses an illuminating system in which two line light sources positioned respectively at focal points in two separate ellipses cooperate with two circular cylindrical mirrors and elliptical sections to provide a line of high luminous intensity with an open path between the elliptical sections for the reflected light. Interference filters are used to reflect infrared radiation away from the document being copied.